1. Field of the Invention
The present invention relates to detection elements for measuring physical properties (flow amount, flow rate, etc.) of fluids by utilizing heat exchanging or heat transmission phenomenon. The invention also relates to a process for producing the same.
2. Related Art Statement
For example, a detection element is formerly known as a sensor for measuring the flow amount of sucked air as shown in FIG. 9. Such a detection element is produced as follows:
First, a thin film 2 made of platinum, nickel or the like is formed as a resistor on the outer surface of a cylindrical base body, for example, of a cylindrical long alumina pipe by a physical or chemical means such as vapor deposition, plating or sputtering, and this long alumina pipe is cut to a given length as shown in FIG. 9. Then, tip portions of metallic lead wires 5 are inserted into a hollow space 1b, and are fixed to the alumina pipe 1 with a platinum paste 24 and a glass paste 34 (only the platinum paste may be used).
The platinum paste layer 24 is provided on an end face 1c of the alumina pipe 1, and fixed to the metallic lead wire 5. On the other hand, as shown in an enlarged view of FIG. 9(b), since an end portion of the platinum paste layer 24 contacts the electrical resistor layer 2, the metallic lead wires 5 are electrically connected to the electric resistor layer 2.
However, since the end face 1c of the alumina pipe 1 is formed in such a conventional detection element by cutting, this cut end face 1c and the outer peripheral surface 1d forms an acute right angle. Accordingly, when the platinum paste layer 24 is fired, crack lines 40 grow as shown by broken lines at an end portion of the platinum paste layer 24 because of firing shrinkage. Consequently, electrical conduction becomes poor, and an adverse effect (increased variations in temperature coefficient of resistance and decreased temperature coefficient of resistance) occurs in terms of a temperature coefficient of resistance (T.C.R.) of the detection element.
In order to prevent such poor electrical conduction, a detection element is proposed, in which a platinum paste layer 44 is greatly heaped in lateral and vertical directions as shown in FIG. 10. However, in this case, a connection between the lead wire 5 and the alumina pipe 1 becomes so bulky that heat capacity of the detection element becomes greater to lower the response speed or the like.